The head of NATO cited the Manchester bombing as evidence that member states of the international coalition are not doing enough to fight ISIS and other terrorist groups.

Jens Stoltenberg, the secretary-general of NATO (the North Atlantic Treaty Organization), said Wednesday that the suicide bombing on the Manchester Arena in Northern England that killed at least 22 and left more than 100 injured underscores the importance of standing together in the fight against terrorism.

“I expect NATO allies to step up and agree to do more in the fight against terrorism, not least because of the attack we saw in Manchester,” Stoltenberg said at a press conference in Brussels.

President Trump landed in Belgium on Wednesday on the eve of a NATO summit where terrorism is expected to be at the top of the agenda. Trump wants NATO to become an official member of the U.S.-led coalition against ISIS.

Trump berated NATO during the campaign, declaring it “obsolete” and not focused enough on the battle against terror. But he has since warmed to the organization, a transatlantic military alliance initially formed to counterbalance the threat of the Soviet Union. “I said it was obsolete. It’s no longer obsolete,” Trump said in April, shortly after he approved of Montenegro joining the alliance — a move that Russia opposed.

All 28 members of NATO have already joined the alliance against the so-called Islamic State, but Stoltenberg insisted that NATO’s official involvement would improve counter-terrorism cooperation and organization.

“Many allies would like to see NATO as a full member of the coalition [to defeat ISIS] for two reasons,” he said. “Partly because it sends a strong and clear message of unity in the fight against terrorism, and especially in light of the terrorist attacks in Manchester, I think it is important to send this message of unity against terrorism.”

Another reason certain members want NATO to join the coalition, he continued, involves burden sharing. In 2014, NATO members pledged to gradually increase their individual contributions to defense spending to 2 percent of GDP. Stoltenberg said NATO has made progress on the front after years of decline, with military spending rising by billions last year alone.

The Manchester bombing on Monday targeted the young fans of American pop singer Ariana Grande following a concert. British Prime Minister Theresa May said that many victims were children and raised the country’s official terror threat to critical, which is the highest level.

A message is written on the pavement in Manchester, England, Tuesday May 23, 2017, the day after the suicide attack at an Ariana Grande concert that left 22 people dead as it ended on Monday night. (Photo: Kirsty Wigglesworth)

For Stoltenberg, the tragedy reinforced his belief that European and North American democracies must double down on their efforts to thwart terrorism throughout the world.

“The attacks were brutal, and they deliberately targeted children, young people and families,” Stoltenberg said. “For me this just underlines the importance of standing together in the fight against terrorism.”